1. Field of the Invention
The present invention relates to data transmission. More particularly, the present invention relates to an apparatus and method for data transmission in a power managed state, in a wireless local access network, and a system therefor.
2. Description of the Related Art
In recent years, as portable terminals have become more widely used for wireless communication, many studies have been made for improving their performance and functions. In particular, with the advance of communication technology, data, as well as a voice call, can be transmitted. In a portable terminal having a limited power capacity, a method for reducing power consumption has drawn engineers' interest due to the increased power consumption when transmitting data, i.e., a call related to packet switching.
There are a variety of technologies to reduce power consumption, used in a Wireless Local Access Network (WLAN). A Power Save (PS) mode technique, which is one of them, manages the power of a WLAN module that transmits and receives data to and from an Access Point (AP) in order to perform wireless local communication. In the PS mode, a WLAN module operates in an active state if data are received from an AP and maintains a standby state to reduce power consumption if no data are received. This mode periodically checks the AP connected with a wireless LAN module and maintains an active state or a standby state according to whether data are received.
In another conventional method for reducing power consumption in a portable terminal, a Central Processing Unit (CPU) for processing data is maintained in a standby state and is switched to an active state as occasion demands. An application example of this method is a Wake on WLAN, which is hereinafter called a WoW.
However, a portable terminal using this WoW function suffers a problem in that, since an active state and a standby state of a CPU are not inconsistent with those of a wireless LAN module that transmits/receives data to/from an AP to perform wireless local communication, it cannot process data transmitted from the AP. That is, if a CPU is in a standby state and the AP has data transmitted to a portable terminal operating in a PS mode, a wireless LAN module of the portable terminal switches a standby state of the portable terminal to an active state. After that, this state change is reported to the AP, and the AP transmits data to the portable terminal. That is, the data may be transmitted from the AP to the portable terminal before the CPU for processing data switches its standby state to an active state. In that case, the data, received by the portable terminal before the state of the CPU has been switched to an active state, are not processed by the CPU, even though the data must be processed in the CPU. Therefore, it is necessary that a portable terminal operating in a PS mode receives data after the state of the CPU is completely switched to an active state so that smooth data communication can be performed between the portable terminal and the AP.
Accordingly, there is a need for an improved apparatus and method in a WLAN for efficiently transmitting data and managing power.